Hydraulic pump with double direction of rotation

ABSTRACT

A hydraulic pump with two rotation directions has axial pistons bearing against a swashplate, the pump with a head having two chambers to be connected to a high-pressure circuit and to a low-pressure circuit. A port plate in the form of a flat plate is arranged between a rotary barrel and the head and has two identical ports passing through the thickness of the flat plate. The port plate pivots about an axis to be able to occupy two angular positions according to the direction of rotation of the pump. The pump has a hydraulic-control device for controlling the angular position of the port plate and is able automatically to bring about a change in angular position of the port plate when the direction of rotation of the pump is reversed, under the effect of a pressure differential between the two chambers of the head.

The present invention relates to a hydraulic pump with axial pistonsbearing against a swashplate and with porting by means of a port plate,said pump being able to rotate in both directions of rotation, and inparticular to a device for automatically controlling the port plate.

As is known, pumps with axial pistons and port plates comprise, behindthe pistons, a planar surface referred to as the port plate, into whichare engraved two curved ports intended to perform the porting, one ofthe ports being used for intake and the other for delivery.

Because the construction of a pump ported by a planar port plate, withtwo directions of rotation, requires ports that are identical so thatthey can alternately become an intake port or a delivery port, dependingon the direction of rotation chosen by the user, it is necessary, inorder not to detract from the performance of the pump, to adjust theangular position of said port plate by an angle X so as to optimize theangular position thereof, this entailing means that allow an offset X inboth directions about the axis of rotation thereof.

In known pumps of this kind, the change in angular position of the portplate is performed manually by the user.

Such a mechanism for manually changing the angular position of the portplate is described, for example, in French patent applicationFR-A1-2965311.

U.S. Pat. No. 3,227,095 discloses, in FIG. 16, a reversible pump. Aninternal ring 286 and an external ring 296 slide rotationally in twomutually opposite directions under the effect of the overpressurepresent on the delivery side, so as to reduce the intake cavity I andenlarge the delivery cavity E. The delivery cavity E and the intakecavity I are defined between the two rings 286 and 296 and between thecrossover segments 288 and 298 borne respectively by these two rings.

FR 2 119 108 describes a pump with axial pistons bearing against aswashplate. This pump is not reversible. The port plate 5 is fixed tothe cover 12 of the pump in an angular position that cannot be altered.

It is an object of the present invention to provide a pump equipped withan automatic device for changing the angular position of the port plate.

To do that, the invention proposes a hydraulic pump with two directionsof rotation, comprising axial pistons bearing against a swashplate, thepump comprising a rotary barrel rotated by a shaft and bearing cylindersin which the pistons slide, the pump comprising a head comprising twochambers which are intended respectively to be connected to ahigh-pressure circuit and to a low-pressure circuit, the pump portingbeing performed by a a port plate having two identical ports arrangedfacing two chambers of the head and able to constitute an intake portand a delivery port in each direction of rotation of the pump, eachcylinder being equipped at its base with an orifice which passes insuccession past the intake port and the delivery port as the barrelrotates, said port plate being able to pivot about an axis so as to beable to occupy two angular positions according to the direction ofrotation of the pump, characterized in that the pump comprises ahydraulic-control device for controlling the angular position of theport plate and able automatically to bring about a change in angularposition of the port plate when the direction of rotation of the pump isreversed, under the effect of the pressure differential between the twochambers of the head; and the hydraulic control device comprises a freepiston mounted in a cylinder which is connected at each of its ends toone of the two chambers of the head.

Such a piston may be coupled to the port plate by any suitable means fordriving it about its axis. According to one embodiment, the free pistonis provided with a finger the end of which is engaged in a housingformed at the periphery of the port plate.

The invention will be better understood, and further objects, details,features and advantages thereof will become more clearly apparent duringthe course of the following description of one particular embodiment ofthe invention, given solely by way of nonlimiting illustration withreference to the attached drawings. In these drawings:

FIG. 1 is a view in longitudinal section of a pump with two directionsof rotation and axial pistons borne by a rotary barrel and the rear endof which rests against a port plate.

FIG. 2 is an overall perspective view of the pump of FIG. 1 set up forrotating in the clockwise direction, viewed from the head end.

FIG. 3 is a view similar to FIG. 2, the pump being set up for rotatingin the counterclockwise direction.

FIG. 4 is a perspective view in section on IV-IV of FIG. 1, showing apiston for the angular control of the port plate, said piston being in afirst position corresponding to a rotation in counterclockwisedirection.

FIG. 5 is a view similar to FIG. 4, the control piston being in itssecond position corresponding to rotation in the clockwise direction.

FIG. 6 is an enlarged perspective view in section on VI-VI of FIG. 4 ofthe pump head, illustrating the position of the components when the pumpis rotating in the counterclockwise direction.

FIG. 7 is an enlarged perspective view in section on VII-VII of FIG. 5of the pump head, illustrating the position of the components when thepump is rotating in the clockwise direction.

With reference to FIG. 1, which is a schematic axial section through thebody of a variable-capacity pump, it may be seen that the pistons 1 ofthe pump bear against a swashplate 2 of which the information withrespect to the axis of the pump is variable and controlled by twoactuators 5 and 6 working in opposition. Because the pistons 1 of thepump bear against the swashplate 2, the inclination of the latterdetermines the stroke of the pistons and therefore the capacity of thepump. This type 20 of pump is referred to as a variable-displacementpump or a variable-capacity pump.

Each piston 1 slides in a cylinder la which bears against the port plate3. The port plate 3 is a planar metal plate positioned between therotary barrel 20 and the head 40 and pierced in the thickness directionwith two kidney bean ports 22 and 23 (FIG. 7). The cylinders 1 a areborne by a rotary barrel 20, rotated by a shaft 21. Each cylinder isprovided at its base with an orifice 4 which, when the barrel rotates,passes successively past the ports 22 and 23 (FIG. 7) of the port plate3.

With reference to FIGS. 2 and 3, the head 40 of the pump is pierced withtwo similar ducts used alternately, one of them as a delivery duct 41and the other as an intake duct. An intake flange 43 is mounted on thehead 40 at the intake duct in FIGS. 2 and 3. The roles of two ducts areswapped over when the direction of rotation of the pump is reversed.

Automatic control of the angular position of the port plate will now bedescribed. This is illustrated in FIGS. 4 to 7.

The port plate 3, the overall shape of which is that of a ring piercedwith a central hole for the passage of the shaft 21 and having anessentially circular exterior contour, is mounted with freedom to rotateabout the axis of the shaft 21 of the pump. The port plate 3, providedwith its two identical ports 22 and 23 and mounted to rotate on theshaft 21 has, at its periphery 35, a U-shaped housing 36. Positioned inthis housing 36 is the end of a finger 37 which is borne by a piston 38which slides freely in its cylinder 39.

When liquid under pressure is introduced on one side of the cylinder 39,the piston 38 is driven until it comes into abutment against theopposite end of the cylinder 39 and is held there by the pressure. Thismovement of the piston 38 sets the port plate 3 in a rotationalmovement. The two opposite positions of abutment of the piston 38 definethe two extreme angular positions of the port plate 3 (X and −X), whichcorrespond, one of them to rotation in the clockwise direction (FIGS. 2,5 and 7) and the other to the rotation in the counterclockwise direction(FIGS. 3, 4 and 6).

FIGS. 4 and 5 depict the pump head without the port plate 3 but with theintake orifice 48 and delivery orifice 41, which are alternately theright-hand orifice and the left-hand orifice of the pump head 40according to the connections made in accordance with FIGS. 2 and 3. Thecylinder 39 accommodating the free piston 38 is formed in the head 40,above two symmetric chambers 49 situated respectively facing theorifices 48 and 41.

Each of the two chambers 49 communicates via a passage 42 with arespective end of the cylinder 49. Thus, under the effect of thehydraulic pressure, the piston 38 is always kept in abutment at the endof the cylinder 39 that communicates with the chamber 49 situated at thelow pressure, namely the intake side 48, and held away from that end ofthe cylinder 39 that communicates with the chamber 49 situated at thehigh pressure, namely the delivery side 41.

In FIG. 5, which corresponds to rotation of the pump in the clockwisedirection, the orifice 48 is the intake orifice, the orifice 41 beingthe delivery one. The pressure arrives via the passage 42 on theleft-hand side of the cylinder 39 and the piston 38 is pushed to theright until it comes into abutment against the right-hand end of thecylinder 39 where it is held by the pressure. This movement of thepiston 38 causes the port plate 3 to pivot into the position depicted inFIG. 7 (angle X).

In FIG. 4, which corresponds to the rotation of the pump in thecounterclockwise direction, the orifice 41 is the delivery orifice, theorifice 48 being the intake orifice. The pressure arrives via thepassage 42 on the right-hand side of the cylinder 39 and the piston 38is pushed to the left until it comes into abutment with the left-handend of the cylinder 39 where it is held by the pressure. This movementof the piston 38 causes the port plate 3 to pivot into the positiondepicted in FIG. 6 (angle −X)

Thus, the change in the angular adjustment (X or −X) of the port plate 3is performed with no intervention by the user other than connecting upthe inlet and outlet orifices of the pump head 40.

Each end of the piston 38 is equipped with an elbowed internalpassageway 50 connecting the end face of the piston 38 to the lateralface of the piston 38 in line with the passageway 42, so that thehydraulic pressure from the passageway 42 can be transmitted to thecorresponding end of the cylinder 39 when the pump direction isreversed, thus causing the piston 38 to begin its axial movement.

As visible in FIGS. 4 and 5, supply ducts 51 and 52 formed in the head40 lead from the cylinder 39 in the opposite direction to thepassageways 42 toward the pump control unit (not depicted) to supplythis control unit with hydraulic pressure. Each of the ducts 51 and 52is fitted with a ball valve 53 which opens only on the side of the pumpdelivery pressure.

Although the invention has been described in conjunction with oneparticular embodiment it is quite clear that it is not in any wayrestricted thereto and that it comprises all technical equivalents ofthe means described and combinations thereof where these fall within thescope of the claimed invention.

The use of the verbs “comprise”, “have” or “include” and conjugatedforms thereof does not exclude the presence of elements or steps otherthan those listed in a claim. The use of the indefinite article “a” or“an” for an element does not, unless mentioned otherwise, preclude therebeing a plurality of such elements.

In the claims, any reference sign between parentheses must not beinterpreted as limiting the claim.

1. A hydraulic pump with two directions of rotation, comprising axialpistons (1) bearing against a swashplate (2), the pump comprising arotary barrel (20) rotated by a shaft (21) and bearing cylinders (1 a)in which the pistons (1) slide, the pump comprising a head (40)comprising two chambers (49) which are intended respectively to beconnected to a high-pressure circuit and to a low-pressure circuit, thepump porting being performed by a port plate (3) defining an intake portand a delivery port, each cylinder (1 a) being equipped at its base withan orifice (4) which passes in succession past the intake port and thedelivery port as the barrel (20) rotates, the pump comprising ahydraulic-control device (38, 39, 42) for controlling the angularposition of the port plate (3) and able automatically to bring about achange in angular position of the port plate when the direction ofrotation of the pump is reversed, under the effect of the pressuredifferential between the two chambers (49) of the head (40),characterized in that the port plate (3) is produced in the form of aflat plate arranged between the rotary barrel (20) and the head (40),the port plate (3) having two identical ports (22, 23) passing throughthe thickness of the flat plate and arranged facing two chambers (49) ofthe head and able to constitute the intake port and the delivery port ineach direction of rotation of the pump, said port plate (3) being ableto pivot about an axis (21) so as to be able to occupy two angularpositions according to the direction of rotation of the pump, thehydraulic control device comprising a free piston (38) mounted in acylinder (39) which is connected at each of its ends to one of the twochambers (49) of the head (40).
 2. The hydraulic pump as claimed inclaim 1, in which the free piston (38) is provided with a finger (37)the end of which is engaged in a housing (36) formed at the periphery(35) of the port plate (3).
 3. (canceled)